The chicken for sale at your local grocery store isn't like the chicken your grandparents used to eat. They're bigger and more "breasty," says public health journalist Maryn McKenna — and that's by design.

"In the United States, we much prefer to eat white meat, and so we have bred chickens and genetically redesigned chickens in order for them to have a lot of breast meat," McKenna says. She attributes the change in poultry to factors like precision breeding, hormones and nutrition, but adds, "Antibiotics started this process."

Many large poultry farms feed antibiotics to their chickens in an effort to prevent disease. But McKenna says that humans who eat those chickens are at risk of developing not only antibiotic-resistant gastrointestinal infections, but also urinary tract infections as well. She chronicles the use of antibiotics in the poultry industry in her new book, Big Chicken.

McKenna's aim in writing the book is not to scare people away from eating poultry; rather, she hopes to improve the quality of the chicken we consume. "I think meat eating is going to remain with us as a culture," she says. "Therefore, I want to see meat producing get better, get better for the animals and also get safer for us. I do think it's possible to get there."

Interview Highlights

On how feeding antibiotics to chickens can lead to antibiotic-resistant foodborne infections in humans

When we give animals antibiotics, those antibiotics, for the most part, are given in their food and water. So they go into the animal's guts. They make some of those bacteria [in the gut] resistant. ... That bacteriacontaminates [the animal's] meat. We eat the meat. And then we develop the foodborne illnesses that ... happen to be antibiotic-resistant. ...

Because of the consolidation of food production, in which now fewer very large firms are distributing their products over very large spaces, we get very large outbreaks of antibiotic-resistant foodborne illness that can be distributed hundreds and thousands of miles away from where the original farms are.

On how antibiotic-resistant bacteria in chickens can lead to urinary tract infections in women

Sometimes those [antibiotic-resistant] bacteria get out of our digestive systems and travel the short distance to our urinary systems, and then it feels just like a regular UTI. So a woman goes to her doctor and says, "I have a urinary tract infection." And the doctor will give her one of those standard set of antibiotics that are prescribed by medicine, and nothing happens. In other words, the antibiotic doesn't work because the infection is resistant.

But because so many people get UTIs so often — 6 to 8 million UTIs in women in the United States every year — that woman might go back to her doctor and the doctor will presume that she's been re-infected as opposed to the UTI never having been cured at all.

The reason why this is such a problem is that an untreated UTI gets worse and it can climb up the urinary system, into the kidneys, cause a kidney infection. The kidneys are a kind of back door to the circulatory system. So if the bacteria propagate through them, then you're looking at a bloodstream infection, infections in other organ systems, even septic shock, which can be deadly, all tracing back to antibiotic use on farms.

One pretty good estimate now is that of those 6 to 8 million UTIs that occur in women every year in the United States, possibly 10 percent could be foodborne UTIs, could be due to this antibiotic-resistant bacteria traveling from farms — which means 600,000 to 800,000 cases a year in this country.

On what to look for when reading labels on chicken meat

There definitely are things on labels on chicken that you should raise an eyebrow at, if you see them. Things like, for instance, "Raised without hormones," or "Raised cage-free." Well, hormones have never been legal for meat chicken in the United States, and similarly, meat chickens are never raised in cages. So those are both sort of claims that the companies can make that they don't really get any credit for.

A thing to look for is if it says, "No antibiotics ever," or sometimes, "Raised without antibiotics." And, to me, that is as significant a claim as "Organic." In some ways maybe more significant, because one of the weirdnesses of organic regulation in the United States is that the organic standard for meat chicken clicks in on day two of the chicken's life. So that chicken could've gotten antibiotics ... injected into it when it's still in the shell or in its first day of life. And that exposure might have been enough to generate resistant bacteria in that chicken's systems when it's a tiny, fluffy chick, even if it doesn't get antibiotics in the rest of its life.

In 2014, Jim Perdue, who is the chairman of the very large chicken company Perdue Farms, the fourth-largest chicken company in the United States, called a press conference and announced that his family-owned company was turning away from routine antibiotic use. In fact, he said they had been doing this since 2007 and they were almost done with the process.

And now today, three years later, they are functionally 100 percent antibiotic-free — about 98 or 99 percent, depending on the year. That was such a shock to the industry that a number of other companies followed Perdue's lead, both in food production, so other chicken companies like Tyson, for instance, and also in food service, so companies like Chik-Fil-A and Subway and McDonald's and other fast-casual [restaurants] and larger companies.

Why did they do this? I have to say, not because they are explicitly concerned about antibiotic resistance. They did it because they're concerned about the reaction of their consumers. And Perdue themselves say they were getting about 3,000 comments a month from their customers questioning why routine antibiotics had to be used, in expressing discomfort with that process. And being intensely attuned to their customers, they decided to study, to figure out whether they could do away with routine antibiotics in their chickens, and it turns out that they could.

Heidi Saman and Thea Chaloner produced and edited the audio of this interview. Bridget Bentz, Molly Seavy-Nesper and Maria Godoy adapted it for the Web.

This is FRESH AIR. I'm Terry Gross. You probably know that many strains of bacteria have become resistant to antibiotics, making resulting infections difficult to treat. We've been told that resistance is partially a result of doctors overprescribing antibiotics. But it might be more connected to the use of antibiotics in livestock, where the drugs are used to promote growth and prevent the kinds of infections that arise in factory-farm conditions. In the U.S., meat animals consume four times the amount of antibiotics that people do so if doctors are being warned about overprescribing antibiotics, well, what about the livestock industry? That's the kind of question my guest, Maryn McKenna, set out to answer in her new book, "Big Chicken." She focuses on the chicken industry because Americans consume more chicken than any other meat, and the use of antibiotics in livestock started with chicken. But as we'll hear, the chicken industry is starting to change.

Maryn McKenna is a journalist who writes about public health and food policy. Her previous book, "Superbug," was about the crisis caused by antibiotic-resistant bacteria. Maryn McKenna, welcome back to FRESH AIR. Before we get to some of the history of how antibiotics became used in chickens, let's talk about some of the kinds of resistant infections that are hard to treat now because of the livestock industry or maybe specifically because of the chicken industry. For instance, like, we've always known that there are certain gastrointestinal infections that come from eating bad food, bad food that has, you know, bacteria in it. So let's start with those 'cause some of those have become more resistant. So what are some of the concerns about that kind of food poisoning?

MARYN MCKENNA: So the first thing that happens, and the thing that I think people intuitively kind of understand, is that there are foodborne infections, which are basically gut bacteria from animals that reach us as a result of the animals being taken apart and made into meat, right? So the foodborne bacteria, like salmonella and campylobacter and shigella, get to reside in the animals' guts. And when we disassemble those animals, the gut contents get on the meat and then travel to us. When we give animals antibiotics, they go into the animal's guts. They make some of those bacteria resistant, and then the end result is antibiotic-resistant, foodborne illness that can be distributed, you know, hundreds and thousands of miles away from where the original farms are. And in one outbreak that I describe in this book, more than 600 people were made sick by drug-resistant salmonella in 30 states and territories in an outbreak that covered more than 12 months.

GROSS: And, as you say in the book, we usually blame, like, the kitchen of the restaurant for sloppy hygiene that results in food poisoning. But you're saying it's sometimes the animals themselves.

MCKENNA: Right, the animals or the production processes that cause the animals to be raised in the way that they were, that as they're given antibiotics, they become sort of little factories for the production and distribution of antibiotic-resistant bacteria. And that leads to some of the sort of - the kinds of infections that people don't make such an intuitive leap to understanding, which is to say that they're not just foodborne illnesses coming immediately from exposure to the meat, but rather that as that process of resistant bacteria in the animals' guts is happening, some of those resistant bacteria leave the animals as manure while the animals are still alive and then go into the farm environment and get washed away by stormwater, or go into groundwater, or blow away as dust on the wind, or leave on the feet of rodents and insects. And those resistant bacteria widely disseminated through the environment in a way that has no obvious chain of evidence back to the farm where they originated.

GROSS: So am I understanding this correctly that you can come in contact with resistant bacteria that emanates from chickens that have been fed or livestock that have been fed a lot of antibiotics, and they develop immune bacteria in their gut, and some of that comes out in the manure and then the manure can spread it to a wider area? How does the manure spread it, spread the resistant bacteria?

MCKENNA: So if you think of any photograph you may ever have seen of a very, very large livestock farm, there's likely to be either a pile of manure, dry manure, in the case of a chicken farm, or a liquid lagoon of manure in a case of a pig farm or a cattle feed lot. So there are resistant bacteria in that manure, and a variety of things can happen. Possibly, you know, a storm may come and stormwater runoff may wash those bacteria out into other water systems or rinse them down into the groundwater, or the surface of the manure may dry out and dust may carry those bacteria off on the wind. Or, the feet of insects and rodents may carry those bacteria away. There even are some cases on record of farm workers themselves unknowingly picking up that dust and those bacteria and taking them to their homes on their uniforms or on their skin.

GROSS: So how often do scientists think that this happens, that that bacteria is passed along, not just through the meat but through dust or through the water, through clothing?

MCKENNA: Right now I think it's quite hard to predict the probability, and the reason for that is because we don't have good data about the degree to which bacteria are traveling off farms because there's no one who's standing at the perimeter of farms either, you know, measuring the air or measuring the groundwater, or even on a very regular basis measuring the animals themselves, checking them to see how frequently they're harboring resistant bacteria. There's been a push for a number of years to get better data on farms, and the federal authorities just have not been able to get there, haven't been able to get on to farms to check animals routinely. So the data that we have that predicts the probability is all when individual academic researchers have checked, you know, insects around very large farms or residents around very large farms or kids in day care in the towns that are near very large farms. And when they check, they find these bacteria. But is it routine? The data gathering isn't routine to prove it.

GROSS: One of the things that really astonished me in your book is that some infections that you wouldn't think have anything to do with chickens might have something to do with chickens, like UTIs, urinary tract infections. What is the connection between UTIs and resistant bacteria from chickens or livestock?

MCKENNA: This is one of the stories that really astonished me as well, and it's an emerging area of research. There are just a few researchers that have been working on this for more than a decade now elucidating this connection. So we talked a minute ago about how sort of the process of an antibiotic-resistant foodborne illness is that it starts as bacteria in the animals' guts. That bacteria contaminates their meat. We eat the meat, and then we develop the foodborne illnesses that we're fairly used to but they happen to be antibiotic resistant. Well, sometimes we take in those resistant bacteria and nothing immediately happens. They become part of our gut microbiome, part of that community of bacteria that lives in our guts quiescently. But then, and this is particularly true for women because of our anatomy, sometimes those resistant bacteria get out of our digestive systems and travel the short distance to our urinary systems, and then it feels just like a regular UTI.

And so a woman goes to her doctor and says, I have a urinary tract infection. And the doctor will give her one of those standard set of antibiotics that are prescribed by medicine, and nothing happens. And, in other words, the antibiotic doesn't work because the infection's resistant. But because so many people get UTIs so often, 6 to 8 million UTIs in women in the United States every year, that woman might go back to her doctor and the doctor will presume that she's been re-infected as opposed to the UTI never having been cured at all.

The reason why this is such a problem is that an untreated UTI gets worse, and it can climb up the urinary system into the kidneys, cause a kidney infection. The kidneys are a kind of back door to the circulatory system. So if the bacteria propagate through them then you're looking at a bloodstream infection, infections in other organ systems, even septic shock, which can be deadly, all tracing back to antibiotic use on farms. And one pretty good estimate now is that of those 6 to 8 million UTIs that occur in women every year in the United States, possibly 10 percent could be foodborne UTIs, could be due to this antibiotic-resistant bacteria traveling from farms, which means 600,000 to 800,000 cases a year in this country. That's a massive public health burden, a really important problem that's just been sort of hiding in plain sight.

GROSS: So are we running out of treatments - for instance, for UTIs?

MCKENNA: We are. In fact, one of the background conditions that makes this problem of using antibiotics routinely in farm animals so problematic is that we're running out of antibiotics, generally. The backdrop to the rise in antibiotic resistance around the world is that pharmaceutical companies have gotten tired of making antibiotics and having their power taken away by the rapid development of resistance.

If you look at the number of drugs that have been licensed by the FDA over the past couple of decades, there's a really sharp drop-off in antibiotics. So as - if you think of the rise of antibiotic resistance as a kind of game of leapfrog between bugs and drugs, over the decades, the bugs have leapt ahead because we have no new drugs to block their advance. And that is true for the very serious infections that can arise in someone - from something that starts as a resistant UTI, as it is for other drug resistant infections, too.

GROSS: Let me reintroduce you here. My guest is Maryn McKenna. She's the author of the new book "Big Chicken: The Story Of How Antibiotics Created Modern Agriculture And Changed the Way The World Eats" (ph). She's also the author of an earlier book about antibiotic-resistant bacteria. We're going to take a short break, then we'll be right back. This is FRESH AIR.

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GROSS: This is FRESH AIR, and if you're just joining us, my guest is Maryn McKenna. She's a journalist who specializes in public health and food policy. Her new book, "Big Chicken," is about the use of antibiotics in the chicken industry and how that's lead to antibiotic-resistant bacteria that are picked up by people, causing resistant infections in people.

So you write that the chicken industry is actually starting to move away from a reliance on antibiotics, including some of the big chicken companies. Why is that happening?

MCKENNA: This is one of the really interesting parts of this story. And I have to say, it's a part of the story that didn't happen until after I began writing this book, so I had to catch up as events occurred. So in 2014, Jim Perdue, who's the chairman of the very large chicken company, Perdue Farms, the fourth-largest chicken company in the United States, called a press conference and announced that his family-owned company was turning away from routine antibiotic use.

In fact, he said they had been doing this since 2007, and they were almost done with the process. And now today, three years later, they are functionally 100 percent antibiotic free - about 98 or 99 percent, depending on the year. And that was such a shock to the industry that a number of other companies followed Perdue's lead, both in food production - so other chicken companies like Tyson, for instance - and also in food service - so companies like Chick-fil-A, and Subway, and McDonald's and other fast-casual and larger companies.

So why did they do this? I have to say, not because they are explicitly concerned about antibiotic resistance, but they did it because they're concerned about the reaction of their consumers. And Perdue themselves say that they were getting about 3,000 comments a month from their customers questioning why routine antibiotics had to be used and expressing discomfort with that process. And being intensely attuned to their customers, they decided to study, to figure out whether they could do away with routine antibiotics in their chickens, and it turns out that they could.

GROSS: So what was the study like? What did they examine when - what did they have to change in order to cut out antibiotics - because as you point out, the modern chicken farming industry has been built around the use of antibiotics.

MCKENNA: So what they did - and it's actually very elegant. It's a really nice experiment. They chose a bunch of the farms that are contracted to them to raise birds, and they picked farms in different parts of the country - you know, in different microclimates, in different states, and different latitudes and so forth, with different types of barns. And on every farm, they picked two barns that were the same age, so they had sort of a paired set.

And one barn was the control. They didn't change anything in the process there. And then in the other barn, they took the antibiotics out of the chickens' feed. And what they found was that whereas back in the 1940s and '50s when this started, antibiotics might have given farmers a reliable 12-15 percent increase either in the growth of chickens or in shortening of the time in which they were raising chickens, now it can be only about 1 percent, which is effectively a rounding error. It's not something that was worth the expense and the attention. So then Perdue decided to take this recognition and make it part of their regular operation.

And so they asked themselves, well, if we're taking antibiotics out, not just for growth because we're not getting much growth, but also for any kind of prevention against disease, what are the things that we need to do to cause animals' immune systems to be stimulated in ways that antibiotics would otherwise have taken care of?

And the really interesting thing about it is that they themselves say they're going back to older practices that maybe their grandparents, maybe the founder of Perdue, who's the current chairman's grandfather, would've recognized - things like allowing the birds to exercise more, giving them a more pure diet that doesn't include the rendered protein of other slaughtered animals, allowing them to have sunlight on their feathers. They're cutting windows in the sides of the barns.

They also do things like give them a lot of other supplements like herbs, the kind of bacteria that are in yogurt and organic acids, and they use a lot more vaccines. So they've built a sort of structure now around the birds that involves doing other things for them, and those other things don't carry the risk of stimulating the development of resistant bacteria.

GROSS: So it's interesting. Tell me if I'm interpreting this correctly. For years, the livestock lobby and the pharmaceutical lobby kind of blocked any kind of regulations that would limit the use of antibiotics in livestock and chickens, but consumer complaints brought about a big change.

MCKENNA: That's exactly correct, and to me it's one of the fascinating things about this story. So, you know, the first attempt at controlling the use of antibiotics in farm animals in the United States was in 1977, in the early days of the Carter administration. Jimmy Carter went to Washington promising to change Washington with a crew of earnest young reformers, and one of those young reformers was his FDA Commissioner Donald Kennedy, who would go on to become the president of Stanford University after he was effectively chased out of the government. And the reason he was chased out of the government was he tried to make this change. He tried to withdraw the licenses for growth promotion of antibiotics that the FDA had granted in the 1950s, and a very powerful congressman backed by agricultural interests threatened to hold the FDA's entire budget hostage if Kennedy went ahead. And so the White House told Kennedy not to, and Kennedy left government and went back to Stanford.

So there was a stalemate for decades. But out of that stalemate the, you know, science around the risk of antibiotic-resistant bacteria emerging from farms kept moving ahead and ahead. There was more and more evidence. There are now hundreds and thousands of pieces of evidence proving this connection. And eventually, the knowledge of that connection started to filter down to consumers. And starting in, I would say about 2010, first very large hospital and health care systems said that they didn't want to buy meat raised with the routine use of antibiotics because if there were resistant bacteria on it, it would imperil their vulnerable patients, you know, cancer patients and people who'd had organ transplants and people in ICUs. And then they were joined by very large school systems that made essentially the same argument, that this would threaten the kids to whom they're feeding school lunch every day. And then with those big actors, they were joined by chefs who were taking an activist position and by farmers who wanted to see things change and by families of people who had had drug-resistant resistant infections. And all of this consumer movement put together with, you know, with the help of advocacy organizations, I think...

GROSS: This would maybe include certain markets, too, that didn't want to buy chicken that had antibiotics.

MCKENNA: Right, exactly. You know, different small supermarket systems and independent supermarkets and so forth. All of those together created, I think, a climate in which the Obama administration felt it was safe to go out with these FDA regulations, and also created a climate in which the companies themselves could feel that if they made this substantial change in the way they operated, it would be welcomed by their customers and they would be safe in going ahead.

GROSS: My guest is Maryn McKenna, author of the new book, "Big Chicken." After a break, we'll talk about what to look for on the label when you're buying chicken and claims on the label that may be misleading, and Justin Chang will review Richard Linklater's new film, "Last Flag Flying." I'm Terry Gross, and this is FRESH AIR.

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GROSS: This is FRESH AIR. I'm Terry Gross, back with Maryn McKenna, author of the new book, "Big Chicken." It's about how chickens in factory farms came to be fed antibiotics to enhance growth and prevent infection, and how that's contributed to the evolution of antibiotic-resistant bacteria. McKenna is a journalist who writes about public health and food policy. Her previous book, "Superbug," was about the health crisis caused by antibiotic-resistant bacteria. When we left off, we were talking about how some large companies in the chicken industry recently started moving away from antibiotics as a result of consumer pressure.

So when you buy chicken, what do you look for on the label, and what are some of the subtleties in how to read the label (laughter) 'cause there's often subtleties where it's telling you one thing but it's not telling you the complete story.

MCKENNA: Right. There definitely are things on labels on chicken that you should raise an eyebrow at if you see them. For, you know, things like, for instance, raised without hormones or raised cage-free. Well, hormones have never been legal for meat chicken in the United States. And similarly, meat chickens are never raised in cages so those are both sort of claims that the companies can make that they don't really get any credit for. But a thing to look for is if it says, no antibiotics ever, or sometimes, raised without antibiotics. And to me, that is as significant a claim as organic, in some ways maybe more significant because one of the weirdnesses of organic regulation in the United States is that the organic standard for meat chicken clicks in on day two of the chicken's life. So that chicken could have gotten antibiotics injected into it when it's still in the shell or in its first day of life. And that exposure might have been enough to generate resistant bacteria in that chicken's systems when it's a tiny, fluffy chick, even if it doesn't get antibiotics in the rest of its life. And so to me, a label claim of raised without antibiotics is a thing that's really worth looking for.

GROSS: And if it says, raised without antibiotics, it truly means that?

MCKENNA: Yes. I mean, the companies that are making that claim are standing behind it. Now, sometimes there are subtleties. For instance, some companies might say - and this language might change from company to company - raised without human antibiotics, or raised without antibiotics important in human medicine. And the distinction they're making there is that they might still be using some antibiotics for disease prevention, but there's a category of antibiotics that are used in poultry-raising that are effectively not significant to us because if a resistant infection developed, it wouldn't be one that we would need to treat anyway. We don't use that drug, and so I feel like we're kind of safe.

GROSS: So, you know, the use of antibiotics went hand in hand with the growth of the chicken industry because the way the chicken industry grew kind of depended on keeping the chickens in close quarters, bred to just be stationary and fat, and they needed antibiotics to prevent them from getting infections in these conditions, and they used antibiotics to help them grow. So anyway so the growth of the industry and antibiotics went hand in hand. How have chickens changed as a result? You compare the chickens of today that were bred to survive those circumstances and to be kind of large for consumers (laughter). You compare those to the chickens that preceded the industrialization of chickens.

MCKENNA: So the quickest way to say it is that the meat chickens that we eat today get to twice the weight in half the time as chickens 50 or 60 years ago. A chicken, a modern chicken today, a meat chicken is a very large, docile kind of unbalanced very breast-y bird because in the United States, we much prefer to eat white meat. And so we have bred chickens and sort of genetically redesigned chickens in order for them to have a lot of breast meat. Chickens didn't used to be that way. If you thought of the, you know, if you could imagine the chicken that our grandparents or great-grandparents would have had out their back doors back when chickens were kept mostly as engines for egg production rather than as things that were meat in themselves, they would have been pretty upright, pretty scrawny, very energetic, able to run around after their chicks and flap up into trees to evade predators, and often multicolored, as well (laughter). And so though antibiotics, you know, sort of started this process of the change in chicken, there were other things along the way - precision breeding and precision nutrition - that reshaped the chicken so it became this docile, white-feathered, not exercising block of protein that just sits in a barn and gets up and eats and drinks, and sits back down again.

GROSS: Can you tell the difference in taste between chickens in industrial farms that were raised with antibiotics and chickens that really were allowed to be free-range and were not fed antibiotics?

MCKENNA: Absolutely. You can taste it, and you can see it. A chicken that has been able to - that has been allowed to feed itself, that has been able to walk around a pasture or even a barnyard, to flap, to move its wings, it will have more flavor in its flesh. And they often are a little bit more pink as well because they've had more blood fusing their muscles.

GROSS: So where does the use of antibiotics in chickens begin? Whose idea was that?

MCKENNA: So if there's a villain in this story, or at least an anti-hero, it's a scientist named Thomas Jukes, who's an emigre Brit who migrates to California in the '30s and then ends up working in New York state for one of the first antibiotic manufacturers, a company called Lederle Laboratories, which is part of a larger company, called American Cyanamid. And in 1948, Jukes is tasked with trying to find a cheap supplement, a nutritional supplement to add to the cheap feed that producers are now giving livestock in the aftermath of the destruction of the food system in World War II. And so Jukes sets up an experiment in which he takes a bunch of chicks and he divides them up, and he gives the different groups different supplements - crystalline vitamins, and cod liver oil and distiller's grains into one of those groups. He gives the dried remains of the drug that his company is making, chlortetracycline, or aureomycin, which is one of the first antibiotics.

And when he comes to weigh them all on Christmas Day in 1948, Christmas Day because he's given his lab assistant the day off and he goes and does it himself, he discovers that the chicks that got the dried remains of his company's antibiotic gain more weight than any other chickens in his experiment. And he pretty quickly realizes that what's actually gone on is that in those dried leftovers there are tiny doses of the antibiotic that the company is making, and that gives that company, Jukes and his company, literally the barratries, enough evidence to start selling their antibiotic as a livestock feed supplement. And within five years, American farmers are giving their livestock 500,000 pounds of antibiotic a year. Today of course that's up. It's more than 34 million pounds in the most recent federal data, but it was something that was adopted very, very fast.

GROSS: If you're just joining us, my guest is Maryn McKenna. She's the author of the new book, "Big Chicken." We're going to take a short break, and then we'll be right back. This is FRESH AIR.

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GROSS: This is FRESH AIR. And if you're just joining us, my guest is Maryn McKenna. She's a journalist who writes about public health and food policy. Her new book, "Big Chicken," is the story of how antibiotics were used in chickens and how - what the consequences have been of the use of antibiotics in chickens - the consequences for humans. And she's also the author of an earlier book about antibiotic-resistant bacteria.

So there's a lot of fascinating stories about the use of antibiotics in chickens that we won't have time to tell during the course of this interview. But I'm wondering, like, did you visit a variety of chicken farms - some that seemed really clean, keeping relatively healthy chickens, not using antibiotics and others that were just really bad environments for the chickens?

MCKENNA: So in the process of reporting this book, I went to everything from, you know, very beautiful, green pastured farms with the - in which the birds are outside all the time in the United States and in France. I went to barns that are industrial in scope but are antibiotic-free here in the United States and in the Netherlands. And then I visited a variety of conventional American poultry farmers, both chicken and also Turkey farmers.

And sometimes the birds looked really good, you know? They were healthy and upright. And they were they were white-feathered, and they were kind of bright-eyed. And sometimes the farms did not look so good. And I was seeing a lot of dead chickens as these, you know, shoals of chickens moved back and forth across the barn. There would be dead chickens underfoot as they moved, and It was really dismaying.

GROSS: Would they sell those chickens for food?

MCKENNA: No. I mean, you know, if the birds either are dead when the farmer goes in or if they are ill enough that they need to be culled, which is basically that, you know, they're killed on site - their necks are snapped - they are either composted. Or I think in some other livestock arenas like pigs, for instance, they're sent off to rendering, which is a process by which the protein represented by those bodies gets cooked down into sort of a protein meal that then is fed back to other animals.

GROSS: And you visited slaughterhouses, too, right?

MCKENNA: That's right.

GROSS: What did you learn there about the difference between what's considered a more humane approach to slaughter and a more cruel one?

MCKENNA: So the standard process by which most chickens in the United States are killed is this. They're in their barns, and the chicken catchers, as they're called, come in usually while it's still dark in the middle of the night because it's cooler and the birds are more calm. And they grab the chickens, and they stuff them into wire crates. And those wire crates get put on trucks, and they're stacked many, many layers high.

And if you happen to be out on the road early in the morning in parts of Georgia or parts of North Carolina, you would see these chicken trucks going to the slaughterhouse. You can often see that there's sort of a trail of feathers along the side of the road as they've blown by because the sides of the truck are open.

So they come to the slaughterhouse. They are taken out one by one. The chickens are taken out of those cages, the crates. They are hung upside down by their ankles essentially into shackles on a chain. And then they are taken on this long chain through multiple steps of slaughter. So the first thing that happens is they're dunked in an electrified bath that shocks them. And then...

GROSS: To knock them out?

MCKENNA: ...Their necks are slit. Yes, and then their necks are slit with a knife - a rotating knife. And then they are dunked in scalding water to loosen their feathers. And then they are dumped into a drum that has a lot of rubber fingers on the inside, and they're whirled around to loosen all their feathers. That's the de-feathering. And then once they come out, they are, you know, now naked, dead carcasses.

And they begin the long, long process of being disassembled into pieces of meat, which is more or less sort of automated depending on the size and the degree of capitalization of the slaughter plant. And then, after that they are cooled in one of a variety of ways down from body temperature, down to the sort of temperature at which you would refrigerate them either by being dunked in big water baths or by going through sort of chilling rooms still on the chain.

The thing that is being changed the most rapidly in the United States that already exists in Europe and that is being changed by companies in the U.S. is that once the chickens are caught and put into those crates - the more modern crates are of a slightly different shape than the older ones - they get slotted into a giant tunnel at the slaughterhouse kind of like drawers into a file cabinet. And the drawers proceed slowly along a line in which more and more gases that are not oxygen are pumped into the tunnel so that at the end, the chickens are irreversibly unconscious, and then all the rest of the steps happen one by one.

GROSS: As opposed to shocking them.

MCKENNA: Right. It's considered much more humane because they just sort of slowly go to sleep. And you don't have to take the risk then of their experiencing the being flipped upside down and shackled or possibly of missing the moment at which they are shocked into unconsciousness and still being alive when their throats slit.

GROSS: So between researching and investigating antibiotic-resistant bacteria that come from the livestock industry - between that and going to chicken farms, some of which were not very clean or humane and going to slaughterhouses, do you have trouble eating chicken now?

MCKENNA: So I get asked this question a lot. And I think people are often surprised to find that I am still a meat eater. But in fact, I am. And I want to believe that it's possible to want to interrogate the system by which we produce meat and to ask critical questions about it and still come out at the end believing that it's OK to eat meat.

I know there are plenty of people who will disagree with me, but I think we are hardwired as humans to want to eat meat. And when people don't eat meat, it's because they've made a choice that precedes - in some cases, it proceeds from disgust, but in most cases, I think it proceeds from personal ethics. But it's not because their bodies don't particularly want meat. And so I think meat eating is going to remain with us as a culture, and therefore I want to see meat producing get better - get better for the animals and also get safer for us. And I do think it's possible to get there.

GROSS: How do you deal with the possibility of resistant bacteria in your life? I know you're probably a very smart consumer and buy meat and chicken from animals who have not been fed antibiotics. But you've also written about, you know, other forms of resistant bacteria, including ones that are spread in hospitals. But you know, all these resistant bacteria - they kind of get out in the world. They escape. So how super aware are you in your daily life about the possibility of coming in contact with antibiotic-resistant bacteria, and what do you do to avoid it?

MCKENNA: How do I live my life without being irreversibly paranoid (laughter)?

GROSS: That would be a much shorter way of putting the question that I just asked you, yes.

MCKENNA: So yes, the first thing I do is I make a real effort to buy meat that is raised without the routine use of antibiotics. I read labels, and I do this not just because I want to reduce my risk but also because I want to see that sector of the market expand. And I think that smaller producers, ones that now are able to compete again in the market on the basis of not using antibiotics the way they might not have been able to just on price - I think they probably need my dollars more than the really big companies do. So I spend my money on smaller producers that are antibiotic-free when I can. My budget doesn't always allow it.

And when I bring meat into my kitchen I - you know, I try to make sure that I run my kitchen in a relatively hygienic manner, though certainly I'm not running my kitchen at as though it was a microbiology lab, you know? I'm not fogging everything with gases or dousing it in bleach.

But I try not to take too many antibiotics in my personal life so that if there are any resistant bacteria lurking in my system that I've consumed, I'm not going to start the process of sort of allowing them to multiply and expand. When I am in places where I think bacteria may be more likely to be resistant or where a lot of people have been, I try to keep my hands really clean. If you ever rode an elevator with me, you would notice that I touch the elevator buttons with my knuckles, not with the pads of my fingers because the pads of your fingers are things that you will subsequently use to touch your eyes or your mouth and so forth. And so I want to reduce my exposure that way.

But I do think that there are a limited number of things that any of us can do to reduce our risk because we have let the genie of antibiotic resistance out into the world. And so, you know, maybe what I am doing most to protect against antibiotic-resistant infections is to try to raise awareness of the risk to all of us. And maybe if we all together attempt to reduce the use of antibiotics in all realms - in medicine as well as agriculture - maybe then we will all reduce the risk to all of us of drug-resistant infections that could end our lives or the lives of people we love.

GROSS: Well, thank you for warning us about the risk of antibiotic-resistant infections and for doing more than just using your knuckles on (laughter) elevators. Thank you so much for your reporting and for being a guest on our show.

MCKENNA: Thank you for having me.

GROSS: Maryn McKenna is the author of "Big Chicken." After we take a short break, Justin Chang will review Richard Linklater's new film which stars Bryan Cranston, Steve Carell and Laurence Fishburne. This is FRESH AIR.